The present invention relates to a semiconductor laser array device in which a plurality of semiconductor lasers are arranged in the form of a one-dimensional or two-dimensional array.
Owing to its advantages such as small size, small power consumption and direct modulation, a semiconductor laser has now been extensively employed in such devices as compact discs, video discs and laser printers to substitute for the gas laser. Up to the present time, the semiconductor laser light source is usually used in a number of one in these devices. It can, however, be contrived to use the semiconductor lasers in a plural number as the devices become highly sophisticated and more functional. It has now been urged to provide a semiconductor laser array in which a plurality of semiconductor lasers are arranged in a single package. An example can be found in J. N. Walpole et al., Conference on Laser and Electrooptics, Technical Digest, 1986, pp. 64-65, TUB 2, "Monolithic 2-D Arrays of High-Power GaInAsP/InP Surface-Emitting Lasers".
Among many characteristics, the semiconductor laser has a characteristic in that a change in the temperature causes the laser output to change despite the same current is permitted to flow into the laser. In the above-mentioned optical disc devices and laser printers, in general, the output on one side of the semiconductor laser is detected by a photodetector installed in the vicinity thereof and the electric current is adjusted by feedback control operation so that the detected output becomes constant at all times as disclosed in, for example, Japanese Patent Publication No. 46879/1983.
Even a plurality of semiconductor laser arrays require a feedback control operation to maintain the light outputs at predetermined values. In the semiconductor laser array, however, the individual lasers are arranged at positions maintaining a distance of smaller than 1 mm relative to each other. Furthermore, the laser lights emitted from the semiconductor lasers diverge at a large angle of expansion.
It is therefore difficult to detect light outputs from the individual semiconductor lasers using individual photodetectors.